HABIT TIMELINE CALCULATOR

In the best-known study, by Phillippa Lally and colleagues at University College London (2010), the typical time was 66 days among people whose data fit the researchers' model (UCL's summary calls it the average), and individual times ran from 18 to 254 days. A 2024 review of 20 studies found reported medians of 59 to 66 days and an individual range of 4 to 335 days. The short answer is about two months for many people, with wide variation.

The research doesn't support a fixed 21 days. In the 2010 study, 18 days was the fastest anyone reached their habit plateau, and most people took far longer. Our post on the 21-day habit myth covers where that number came from.

In the 2010 study, missing one opportunity to do the behavior did not materially affect the habit forming. Performing the behavior more consistently was associated with a better fit to the habit curve.

A plan written as a specific situation and a specific response: 'When I finish my morning coffee, I will walk for 20 minutes.' Researchers call these implementation intentions. The Roman Protocol's Daily Ledger is built on the same idea: name the standard, the likely obstacle and your response before the day starts.

The 2024 review reported that frequency, timing, the type of habit, choosing it yourself and preparatory habits all influenced habit strength, with morning practices and self-selected habits generally showing greater strength. Most of the included studies had a high risk of bias, so treat those as early findings.